B. The book interesting...the characters were not too difficult to understand.
Explanation:
Ellipsis are supposed to omit irrelevant information in a sentence. Which means it should not change the meaning of the actual sentence itself.
The original sentence states:
The book was interesting and very complex and not too difficult to understand.
It means that the book is interesting and although it is difficult, it is not too difficult to comprehend. There is only one answer choice that states the overall message that the book is not too difficult to understand. A, C, and D all mention that is is too difficult.
The answer that makes the most sense reading & vocal wise is B. With the rest of the answers, ellipses are used unnecessarily which creates unneeded breaks in the sentence.
